from typing import Optional

from django.contrib.postgres.fields import DateTimeRangeField
from django.db import models
from django.utils import timezone
from django.utils.translation import gettext as _


class CreatedModifiedAbstract(models.Model):

    modified = models.DateTimeField(auto_now=True, verbose_name=_("modified"))
    created = models.DateTimeField(auto_now_add=True, verbose_name=_("created"))

    class Meta:
        abstract = True


class Membership(CreatedModifiedAbstract):
    """
    Tracks that a user has membership of a given type for a given period.
    """

    class QuerySet(models.QuerySet):
        def for_user(self, user):
            return self.filter(user=user)

        def _current(self):
            return self.filter(period__contains=timezone.now())

        def current(self) -> Optional["Membership"]:
            try:
                return self._current().get()
            except self.model.DoesNotExist:
                return None

        def previous(self):
            # A naïve way to get previous by just excluding the current. This
            # means that there must be some protection against "future"
            # memberships.
            return self.all().difference(self._current())

    objects = QuerySet.as_manager()

    class Meta:
        verbose_name = _("membership")
        verbose_name_plural = _("memberships")

    user = models.ForeignKey("auth.User", on_delete=models.PROTECT)

    membership_type = models.ForeignKey(
        "membership.MembershipType",
        related_name="memberships",
        verbose_name=_("subscription type"),
        on_delete=models.PROTECT,
    )

    period = DateTimeRangeField(help_text=_("The duration this subscription is for. "))

    def __str__(self):
        return f"{self.user} - {self.period}"


class MembershipType(CreatedModifiedAbstract):
    """
    Models membership types. Currently only a name, but will in the future
    possibly contain more information like fees.
    """

    class Meta:
        verbose_name = _("membership type")
        verbose_name_plural = _("membership types")

    name = models.CharField(verbose_name=_("name"), max_length=64)

    def __str__(self):
        return self.name